Related Clues:

• Words of warning
• 'Whoops!'
• 'Yikes!'
• Otherwise
• 'Otherwise...'
• 'Oops!'
• If not
• Threatening finale
• 'Here comes trouble!'
• Ultimatum ender
• Unnamed alternative
• Unsettling comment from a pilot
• Bad thing to hear at a checkup
• 'Look out...'
• Apprehension expression